Devices used to convert electrical signals to sound, i.e., "loud speakers", typically use a plurality of interacting magnetic fields to vibrate a sound producing baffle. The magnetic fields may be either opposing or complimentary. Typically a voice coil (electromagnet) is used to convert current flow to magnetism. The voice coil is attached to the baffle and is suspended in a magnetic field generated by a permanent magnet. The voice coil is either pushed into or pulled out of the magnetic field generated by the permanent magnet depending on the electrical polarity of the current impressed upon the voice coil. The vibration thus imparted to the voice coil is transmitted to the baffle. The sound producing baffle is typically a thin flexible diaphragm. The movement of the flexible diaphragm imparts the same vibrations to the surrounding air, thus generating sound. This above principle has been widely used for many years in convention speakers, headphones and microphones.
This conventional loud speaker system has found many applications. However, in some applications it would be preferred to use a system which eliminates some of the structure of the conventional loud speaker, for example, the flexible diaphragm. Flexible diaphragms are typically fibrous paper like material which deteriorates from exposure to the elements, such as moisture and extremes in temperatures.
In addition, the typical speaker system normally requires the use of a remote switch to activate the source of audio signals. These switches must be positioned at a place where they are accessible to those wishing to use the system. This often means that the switch and the wiring required to transmit the signal to the source of audio signals are also exposed to the elements and abuse.
A further characteristic of the conventional speaker system is that it is typically made up of separate elements, e.g., loud speaker baffle, switches and audio signal source, which must be assembled and wired into a complete system, engendering additional expense in installation cost. Such systems are not compact and easily movable from one location to another once installed. To move the installation to another location requires reversal of the installation procedure and subsequent reinstallation.
Applicant has produced a sound producing system which eliminates the conventional speaker baffle. In applicant's device, sound is transmitting to a sounding surface, such as a glass panel, by the use of a rigid vibration producing or transmitting baffle. The vibration transmitting baffle is preferably a semi-rigid material and is positioned in immediate contact with a sounding surface. Typically, applicant's entire device is attached to the sounding surface with the attaching devices and the cone in contact with the sounding surface. Applicant's device is contained in a compact housing and includes a conventional permanent field magnet and an electromagnetic voice coil positioned adjacent to the field magnet and in the influence of the magnetic field generated by the field magnet. The voice coil is connected to the vibration transmitting baffle so that motion of the voice coil is transferred directly to the vibration transmitting baffle.
In applicant's preferred embodiment, the voice coil is mounted coaxially with the vibration transmitting baffle. The vibration transmitting baffle is connected to the voice coil and restrains the motion of the voice coil. Motion of the voice coil is restricted to linear motion along the axis of the voice coil. In this embodiment it is possible to position the voice coil closely adjacent to the field magnet so that the air gap, and resulting losses, are minimized. This close relationship is possible due to the restraining effect of the vibration transmitting baffle which prevents wobble and transverse motion of the voice coil, and prevents contact between the voice coil and the field magnet.
It is a feature of applicant's preferred embodiment that the vibration transmitting baffle is conical in shape. The vibration transmitting baffle converges in an outwardly extending direction. Only a small central portion of the vibration transmitting baffle actually makes contact with the sounding surface. The vibration transmitting baffle is stiffened by the use of ribs so that flexure of the baffle is minimized and precise transference of the vibratory motion from the voice coil through the baffle to the sounding surface is achieved. The vibration transmitting baffle is preferably coaxial with the voice coil, so that its motion coincides as precisely as possible with that of the voice coil.
It is preferred that the housing of applicant's device be formed of some convenient to manufacture material, such as a plastic resin which can be injection molded or fabricated by a similar process. With this construction it is possible to produce a housing in which the vibration transmitting baffle is formed integrally with the housing. In this form, the vibration transmitting baffle can be further stabilized against transverse motion, that is motion transverse to the axis of the voice coil. The housing and vibration transmitting baffle are formed with an integral bellows structure at the juncture between the vibration transmitting baffle and the housing itself. This bellows, which preferably extends completely around the outer periphery of the vibration transmitting baffle, permits translatory motion along the axis of the voice coil and of the vibration transmitting baffle, but resists transverse motion.
Although reference is frequently made to the sound transmitting capabilities of the present sound transducer, it is understood that the transducer may also be used to receive sound. In such case the received sound message is recorded or retransmitted with conventional electronics.
The invention may be further understood by reference to the attached drawings and the following description of the drawings and description of the preferred embodiments.